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Abstract:

Provided is an apparatus for operating interior permanent magnet
synchronous motor by receiving a first current command of a flux
weakening control region I in a system including a detector measuring a
position and a speed of a rotor of an IPMSM, the apparatus including a
feedback unit transmitting over-modulated voltage information to a
correction unit, the correction unit using the rotor speed and the
over-modulated voltage information to correct the first current command
to a second current command of a flux weakening control region II, a
control unit controlling the second current command to output a voltage,
a first limit unit limiting an output of the control unit to a maximum
voltage synthesizable by an inverter unit, and the inverter unit applying
a 3-phase voltage command for following a command torque to the IPMSM
using an output of a voltage limit unit.

Claims:

1. An apparatus for operating interior permanent magnet synchronous motor
(IPMSM) by receiving a first current command of a flux weakening control
region I in a system including a detector measuring a position and a
speed of a rotor of the IPMSM, the apparatus comprising: a feedback unit
transmitting over-modulated voltage information to a correction unit; the
correction unit using the rotor speed and the over-modulated voltage
information to correct the first current command to a second current
command of a flux weakening control region II; a control unit controlling
the second current command to output a voltage; a first limit unit
limiting an output of the control unit to a maximum voltage synthesizable
by an inverter unit; and the inverter unit applying a 3-phase voltage
command for following a command torque to the IPMSM using an output of a
voltage limit unit.

2. The apparatus of claim 1, further comprising a first conversion unit
converting a voltage of the control unit on synchronous reference frame
to a voltage on stationary reference frame using position information of
the rotor received from the detector and outputting the converted voltage
to the first limit unit.

3. The apparatus of claim 1, further comprising a current sensor
measuring a phase current outputted from the inverter unit to the IPMSM.

4. The apparatus of claim 3, further comprising a second conversion unit
converting a phase current on stationary reference frame received from
the current sensor to a current on the synchronous reference frame and
providing the converted current to the correction unit and the control
unit.

5. The apparatus of claim 1, wherein the feedback unit feedbacks the
over-modulated voltage between the output of the control unit and the
voltage synthesized by the inverter unit to the correction unit.

6. The apparatus of claim 5, wherein the feedback unit integrates and
high-pass filters a size of the over-modulated voltage, and transmits the
high-pass filtered size to the correction unit.

7. The apparatus of claim 1, wherein the correction unit comprises a
processing unit correcting the first current command to generate the
second current command in case of flux weakening control region II, and a
second limit unit limiting a size of current from the second current
command.

8. The apparatus of claim 7, wherein the processing unit comprises a
decision unit determining the flux weakening control region II, a
determination unit determining a direction of correction of current
command, a calculation unit calculating a proportional gain using a
current rotor speed and a maximum rotor speed, a third limit unit
limiting a size of the current change, a section defining unit defining a
hysteresis section for dividing the flux weakening control region I and
the flux weakening control region II, and an adding unit outputting the
second current command by adding a reference current to an output of the
section defining unit.

9. The apparatus of claim 7, wherein the second limit unit limits the
second current command to a current range outputtable by the inverter
unit.

10. The apparatus of claim 7, wherein the second limit unit provides a
priority to a d-axis current on the synchronous reference frame relative
to the second current command, outputs the d-axis current within the size
of a rated current on a priority base, and selects a q-axis current
command in a permissible range a balance where a size of d-axis current
is deducted from the rated current.

11. The apparatus of claim 1, wherein the first limiting unit limits an
output of the control unit by using a voltage limit hexagon.

Description:

[0001] Pursuant to 35 U.S.C.§119 (a), this application claims the
benefit of earlier filing date and right of priority to Korean Patent
Application No. 10-2011-0066625, filed on July 5, content of which is
hereby incorporated by reference in their entirety.

BACKGROUND OF THE DISCLOSURE

[0002] 1. Field of Endeavor The present disclosure relates to a motor
driving apparatus, and more particularly to a driving apparatus for
operating an interior permanent magnet synchronous motor at a speed
higher than a rated speed.

[0003] 2. Background

[0004] The information disclosed in this Background of the Invention
section is only for enhancement of understanding of the background of the
invention and should not be taken as an acknowledgement or any form of
suggestion that this information forms the prior art that is already
known to a person skilled in the art.

[0005] A permanent magnet synchronous motor (PMSM) is a high-power and
high-efficiency motor that is widely used as a traction motor in the
fields of electric vehicles including hybrid vehicles, fuel cell
vehicles, and the like, as well as other industries.

[0006] In particular, an interior permanent magnet synchronous motor
(IPMSM) is a synchronous motor having a permanent magnet inserted into a
rotor iron core. The IPMSM has excellent high-speed durability and
drivability, and thus is suitable for use as an electric vehicle motor.
in this application fields, the IPMSM is driven in a torque control mode,
where vector control is performed for independently controlling a flux
current and a torque current.

[0007] Furthermore, the IPMSM used for electric vehicles or hybrid
vehicles is very wide in a driving speed range of a rotor to even include
a flux weakening control region II in the driving regions. The flux
weakening control region II defines a case where a center of a voltage
limit ellipse of the IPMSM is positioned inside a current limit circle.

[0008] In the flux weakening control region II, only the voltage limit
condition affects a driving limit condition of the IPMSM, and because
size of DC-link voltage of an inverter is limited, maximum use of the
voltage limit condition is advantageous in terms of output torque.

[0009] FIG. 1 is a block diagram illustrating a driving system of an
interior permanent magnet synchronous motor according to prior art, where
the system is driven by an inverter embodied by a vector control
independently controlling a flux current and a torque current from an
instruction torque.

[0010] The conventional driving system includes an inverter (101), an
IPMSM (102) and a rotor position detector (103) attached to a rotor of
the IPMSM.

[0011] The inverter (101) receives a command torque to output voltages
(Vas, Vbs, Vcs) capable of being driven by the command torque, and the
rotor position detector (103) calculates or measures a rotor position or
to rotor speed.

[0012] The rotor position calculated or measured by the rotor position
detector (103) is used for coordinate change by coordinate converters
(106, 110), and the rotor speed is used by a current command generator
(104).

[0013] The current command generator (104) outputs a current command on a
synchronous reference frame in response to the command torque, the rotor
speed, and the DC-link voltage of inverter. In case of IPMSM, the current
command generator (104) generally uses two or more 2-D look-up tables,
where the look-up table outputs d and q-axes current commands on
synchronous reference frame relative to an entire driving region.

[0014] A current regulator (105) serves to control the current commands
obtained, from the current command generator (104) to output d and q-axes
voltages on the synchronous reference frame.

[0015] The coordinate converter (106) uses the rotor position information
obtained by the rotor position detector (103) to convert an output
voltage of a current controller (105) to a voltage on a stationary
reference frame.

[0016] A voltage limiter (107) uses an inscribed circle of a voltage limit
hexagon to convert a voltage of the coordinate converter (106) to a
voltage synthesizable by an inverter unit (108). The voltage limit
condition of the voltage limiter (107) is determined by the DC-link
voltage, and the voltage positioned at an outside of the inscribed circle
of the voltage limit hexagon is prevented from being outputted and stays
on the inscribed circle of the voltage limit hexagon.

[0017] The inverter unit (108) is a voltage type inverter including a
power semiconductor such as an IGBT (Insulated Gate Bipolar Transistor)
or a MOSFET (Metal Oxide Semiconductor Field-Effect Transistor), and
supplies the voltage commands (Vas, Vbs, Vcs) for following a command
torque to the IPMSM (102).

[0018] A current sensor (109) is interposed between the IPMSM (102) and
the inverter (108) to measure a phase current applied to the IPMSM (102),
and the current measured by the current sensor (109) is returned as a
feedback to the current command generator (104) and the current
controller (105) M response to the coordinate conversion of the
coordinate converter (110).

[0019] FIG. 2 is an exemplary view illustrating a driving region of the
IPMSM of FIG. 1, where A is a curve of a constant torque, and currents on
d and q-axes on the synchronous reference frame relative to a constant
command torque may have an infinite combination, B is a current limiting
condition of inverter, and C, D and E are examples of voltage limit
condition in response to rotor speed, where the voltage limit condition
is changed by rotor speed, and an increased rotor speed reduces the size
of a voltage limit ellipse to an IF direction.

[0020] The sizes of d and q-axes currents on the synchronous reference
frame controllable by the inverter (101) relative to the constant command
torque are determined in a range satisfying both the current limit
condition and the voltage limit condition. In a case a voltage margin is
sufficient, the voltage limit condition is not affected by the limiting
conditions, such that it would be advantageous to track a current command
driving a MTPA (Maximum Torque Per Ampere) in terms of efficiency of
IPMSM.

[0021] For example, in case a predetermined torque command of A is given,
and a voltage limit condition is given as C, a current command to track a
command torque is determined at G, where G is a driving point for
satisfying the MTPA, and a region where only the current limit condition
influences the driving point is defined as a constant torque region.

[0022] In a case a rotor speed increases to cause the voltage limit
condition to move from C to D, a driving point moves from G to H along an
arrow direction, because G is a current region uncontrollable by an
inverter. Here, a region, where both the voltage limit condition and the
current limit condition influence the driving point, as in the region
where the driving point moves from G to H, is defined as a flux weakening
control region I.

[0023] In a case a rotor speed further increases to cause the voltage
limit condition to move from D to E, the current limit condition can no
longer influence the driving region, and only the voltage limit condition
can influence the driving point.

[0024] Here, a region where only the voltage limit condition influences
the driving point is defined as a flux weakening control region II. The
driving point at the flux weakening control region II moves from H to I
along an arrow direction. Voltage Equations on the synchronous reference
frame of IPMSM (102) are provided as below:

where, a superscript is a synchronous reference frame, a subscript `s` is
a variable of stationary reference frame, `ω.sub.r` is an angular
velocity of rotor, `idsr` and `iqsr` are respectively
stator d and (taxes currents on the synchronous reference frame,
`Vdsr` and `Vqsr` are respectively stator d and
q-axis voltages on the synchronous reference frame,
`λdsr` and `λqsr` are respectively stator
d and q-axes rotor fluxes on the synchronous reference frame, Rs,
Lds and Lqs are respectively stator resistance d and q-axes
inductances.

[0025] A driving limit condition of IPMSM (102) is divided to a voltage
limit condition and a current limit condition, and expressed as under:

(Vdsr)2+(Vqsr)2≦(Vs,max)2
[Equation 3]

(Idsr)2+(Iqsr)2≦(Is,max)2
[Equation 4]

Where, Vs,max defines a size of maximum voltage synthesizable by the
inverter (101), and defines a Is,max or rated current of IPMSM(102).
Vs,max is a maximum voltage synthesizable by the inverter (10) and
influenced by the size of the DC-link voltage `V.sub.dr`, and in a case
the voltage limit condition is selected by the inscribed circle of
voltage limit hexagon as in the voltage limiter (107) of FIG. 1,
Vs,max may have the following value.

V a , max = V d c 3 [ Equation 5 ]
##EQU00002##

[0026] As noted from the foregoing, the IPMSM (102) in the flux weakening
control region II is driven at the MTPV (Maximum Torque Per Voltage)
capable of outputting an available voltage, at a maximum torque.

[0027] The moving process of current command is such that an inductance of
the IPMSM (102) is saturated by the size of the current to have a
non-linear relationship. Thus, the driving of the IPMSM is such that
characteristic of IPMSM is measured in advance (off-line) to prepare at
least two or more 2-D look-up tables, whereby the current command
generator (104) of FIG. 1 generates a current command on the synchronous
reference frame responsive to the constant torque, the driving speed and
the DC-link voltage.

[0028] The 2-D look-up table uses the torque command and the flux
information as input to generate the d and q-axes current command on the
synchronous reference frame. At this time, the flux information is
obtained by dividing the DC-link voltage by rotor speed.

[0029]FIG. 3 is a schematic view illustrating a 2-D look-up table
according to prior art. Referring to FIG. 3, the 2-D look-up tables (301,
302) receive the command torque and an input from a flux calculation unit
(303) to output the d and q-axes current commands on the synchronous
reference frame.

[0030] A feedback current of the current command generator (104) of FIG. 1
and the coordinate converter (110) is inputted to the current limiter
(105). The current limiter (105) is a proportional and integral
controller to synthesize an output voltage as per the following
Equations.

The coordinate converter (106) converts an output voltage of the current
limiter (105) on the synchronous reference frame to a voltage on the
stationary reference frame using the following Equations.

Vdsrs=Vdsrs cos θ-Vqsrs sin θ
[Equation 8]

Vqsrs=Vdsrs cos θ+Vqsrs sin θ
[Equation 9]

[0031] The voltage limiter (107) limits a voltage of the coordinate
converter (106) and outputs the voltage, so that a voltage command can
exist within the inscribed circle of the voltage limit condition
expressed by a hexagon on the stationary reference frame, and the
inverter unit (108) synthesize a voltage of the following. Equations from
the voltage limiter (107) and supplies the voltage to the IPMSM (102).

[0033] Current sensors (109a-109c) measure a phase current between the
inverter unit (108) and the IPMSM (102). The coordinate converter (110)
converts the phase current to as current on the synchronous reference
frame using the following Equations and provides the current to the
current limiter (105) as a feedback.

[0034] However, there is a problem in that performance of the IPMSM
driving system of FIG. 1 deteriorates, because the current command
generator (104) uses a pre-measured look-up table to cause subject
parameters of the IPMSM to change.

[0035] Furthermore, there is another problem in that, even if the subject
parameters of the IPMSM are not changed, the driving performance of motor
is determined by performance of the look-up table, because the look-up
table determines the performance of an entire driving region.

[0036] There is still another problem in that a voltage utilization rate
of the inverter decreases to thereby decrease the output torque, because
amount of voltage synthesized by the inverter is limited by the inscribed
circle of the voltage limit hexagon.

[0037] It is, therefore, desirable to overcome the above problems and
others by providing an improved apparatus for operating the interior
permanent magnet synchronous motor.

SUMMARY OF THE DISCLOSURE

[0038] This section provides a general summary of the disclosure, and is
not a comprehensive disclosure of its full scope or all of its features.

[0039] The present disclosure has been made to solve the foregoing
problem(s) of the prior art, and therefore an object of certain
embodiments of the present invention is to provide an apparatus for
operating interior permanent magnet synchronous motor robust in parameter
change by reducing dependency on look-up table during a high speed
driving of an IPMSM, increasing a voltage utilization rate of an
inverter, following a command torque to a maximum and generating a
current command following the command torque to the maximum.

[0040] In one general aspect of the present disclosure, there is provided
an apparatus for operating interior permanent magnet synchronous motor
(IPMSM) by receiving a first current command of a flux weakening control
region I in a system including a detector measuring a position and a
speed of a rotor of the IPMSM, the apparatus comprising: a feedback unit
transmitting over-modulated voltage information to a correction unit; the
correction unit using the rotor speed and the over-modulated voltage
information to correct the first current command to a second current
command of a flux weakening control region II; a control unit controlling
the second current command to output a voltage; a first limit unit
limiting an output of the control unit to a maximum voltage synthesizable
by an inverter unit; and the inverter unit applying a 3-phase voltage
command for following a command torque to the IPMSM using an output of a
voltage limit unit.

[0041] Preferably, but not necessarily, the apparatus further comprises a
first conversion unit converting a voltage of the control unit on
synchronous reference frame to a voltage on stationary reference frame
using position information of the rotor received from the detector and
outputting the converted voltage to the first limit unit.

[0042] Preferably, but not necessarily, the apparatus further comprises a
current sensor measuring a phase current outputted from the inverter unit
to the IPMSM.

[0043] Preferably, but not necessarily, the apparatus further comprises a
second conversion unit converting a phase current on stationary reference
frame received from the current sensor to a current on the synchronous
reference frame and providing the converted current to the correction
unit and the control unit.

[0044] Preferably, but not necessarily, the feedback unit feedbacks the
over-modulated voltage between the output of the control unit and the
voltage synthesized by the inverter unit to the correction unit.

[0045] Preferably, but not necessarily, the feedback unit integrates and
high-pass filters a size of the over-modulated voltage, and transmits the
high-pass filtered size to the correction unit.

[0046] Preferably, but not necessarily, the correction unit comprises a
processing unit correcting the first current command to generate the
second current command in case of flux weakening control region II, and a
second limit unit limiting a size of current from the second current
command.

[0047] Preferably, but not necessarily, the processing unit comprises a
decision unit determining the flux weakening control region II, a
determination unit determining a direction of correction of current
command, a calculation unit calculating a proportional gain using a
current rotor speed and a maximum rotor speed, a third limit unit
limiting a size of the current change, a section defining unit defining a
hysteresis section for dividing the flux weakening control region I and
the flux weakening control region II, and an adding unit outputting the
second current command by adding a reference current to an output of the
section defining unit.

[0048] Preferably, but not necessarily, the second limit unit limits the
second current command to a current range outputtable by the inverter
unit.

[0049] Preferably, but not necessarily, the second limit unit provides a
priority to a d-axis current current on the synchronous reference frame
relative to the second current command, outputs the d-axis current within
the size of a rated current on a priority base, and selects a q-axis
current command in a permissible range a balance where a size of d-axis
current is deducted from the rated current.

[0050] Preferably, but not necessarily, the first limit unit limits an
output of the control unit by using a voltage limit hexagon.

[0051] The apparatus for operating interior permanent magnet synchronous
motor according to the present disclosure has an advantageous effect in
that a difference between two voltages is minimized using a difference
between an output voltage of a current control unit and a voltage
actually synthesized by an inverter unit and dispensing with a
prior-prepared look-up table, all the voltage limit hexagons are used to
increase a DC-link voltage utilization rate of the inverter unit relative
to size of the voltage synthesized by the inverter unit, and a current
command is corrected to a direction holding a torque at a predetermined
level, whereby a maximum torque can be followed even when an IPMSM is
driven at a high speed.

[0052] Particular and preferred aspects of the present disclosure are set
out in the accompanying independent and dependent claims. Features from
the dependent claims may he combined with features of the independent
claims and with features of other dependent claims as appropriate and not
merely as explicitly set out in the claims.

[0053] Although there has been constant improvement, change and evolution
of devices in this field, the present concepts are believed to represent
substantial new and novel improvements, including departures from prior
practices, resulting in the provision of more efficient, stable and
reliable devices of this nature.

[0054] The above and other characteristics, features and advantages of the
present disclosure will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings, which
illustrate, by way of example, the principles of the invention. This
description is given for the sake of example only, without limiting the
scope of the invention. The reference figures quoted below refer to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to explain the principle of the present disclosure, some
accompanying drawings related to its preferred embodiments are below
reported for the purpose of illustration, exemplification and
description, although they are not intended, to be exhaustive. The
drawing figures depict one or more exemplary embodiments in accord with
the present concepts, by way of example only, not by way of limitations.
In the figures, like reference numerals refer to the same or similar
elements.

[0056] Thus, a wide variety of potential practical and useful embodiments
will e more readily understood through the following detailed description
of certain exemplary embodiments, with reference to the accompanying
exemplary drawings in which:

[0057] FIG. 1 is a schematic block diagram illustrating an 1.PMSM
according to prior art;

[0058] FIG. 2 is an exemplary view illustrating a driving region of IPMSM
of FIG. 1;

[0059]FIG. 3 is a schematic block diagram illustrating a 2-D look-up
table according to prior art;

[0060]FIG. 4 is a schematic block diagram illustrating an apparatus for
operating an IPMSM according to an exemplary embodiment of the present
disclosure;

[0061] FIG. 5 is a schematic view illustrating a concept of Equation 25
according to an exemplary embodiment of the present disclosure;

[0062]FIG. 6 is a detailed constructional view illustrating a current
command correction unit of FIG.4 according to an exemplary embodiment of
the present disclosure;

[0063]FIG. 7 is a detailed constructional view illustrating a current
command processing unit of FIG. 6 according to an exemplary embodiment of
the present disclosure; and

[0064] FIG. 8 is a detailed constructional view illustrating a current
command limiter of FIG. 6 according, to an exemplary embodiment of the
present disclosure.

DETAILED DESCRIPTION

[0065] The disclosed embodiments and advantages thereof are best
understood by referring to FIGS. 1-8 of the drawings, like numerals being
used for like and corresponding parts of the various drawings. Other
features and advantages of the disclosed embodiments will be or will
become apparent to one of ordinary skill in the art upon examination of
the following figures and detailed description. It is intended that all
such additional features and advantages be included, within the scope of
the disclosed embodiments, and protected by the accompanying drawings.
Further, the illustrated figures are only exemplary and not intended to
assert or imply any limitation with regard to the environment,
architecture, or process in which different embodiments may be
implemented. Accordingly, the described aspect is intended to embrace all
such alterations, modifications, and variations that fall within the
scope and novel idea of the present invention.

[0066] Meanwhile, the terminology used herein is for the purpose of
describing particular implementations only and is not intended to be
limiting of the present disclosure. The terms "first," "second," and the
like, herein do not denote any order, quantity, or importance, but rather
are used to distinguish one element from another. For example, a second
constituent element may be denoted as a first constituent element without
departing from the scope and spirit, of the present disclosure, and
similarly, a first constituent element may be denoted as a second
constituent element.

[0067] As used herein, the terms "a" and "an" herein do not denote a
limitation of quantity, but rather denote the presence of at least one of
the referenced item. That is, as used herein, the singular forms "a",
"an" and "the" are intended to include the plural forms as well, unless
the context clearly indicates otherwise.

[0068] It will be understood that when an element is referred to as being
"connected" or "coupled" to another element, it can be directly connected
or coupled to the other clement or intervening elements may be present.
In contrast, when an element is referred to as being "directly connected"
or "directly coupled" to another element, there are no intervening
elements present.

[0069] It will be further understood that the terms "comprises" and/or
"comprising," or "includes" and/or "including" when used in this
specification, specify the presence of stated features, regions,
integers, steps, operations, elements, and/or components, but do not
preclude the presence or addition of one or more other features, regions,
integers, steps, operations, elements, components, and/or groups thereof.

[0070] Also, "exemplary" is merely meant to mean an example, rather than
the best. If is also to be appreciated that features, layers and/or
elements depicted herein are illustrated with particular dimensions
and/or orientations relative to one another for purposes of simplicity
and ease of understanding, and that the actual dimensions and or
orientations may differ substantially from that illustrated.

[0071] That is, in the drawings, the size and relative sizes of layers,
regions and/or other elements may be exaggerated or reduced for clarity.
Like numbers refer to like elements throughout and explanations that
duplicate one another will be omitted. As may be used herein, the terms
"substantially" and "approximately" provide an industry-accepted
tolerance for its corresponding term and/or relativity between items.

[0072] Hereinafter, an apparatus for operating an IPMSM according to the
present disclosure will be described in detail with reference to the
accompanying

[0073]FIG. 4 is a schematic block diagram illustrating an apparatus for
operating an IPMSM according to an exemplary embodiment of the present
disclosure.

[0074] Referring to FIG. 4, an apparatus for operating an IPMSM comprises
an inverter (10) including a current command correction unit (11), a
voltage feedback unit (12), a current controller (13), a voltage
coordinate converter (14), a voltage limiter (15), an inverter unit (16),
current sensors (17a-17c), and a current coordinate converter (18), and a
rotor position detector (30).

[0075] The inverter (10) receives a current command of a flux weakening
control region and outputs voltages Vas, Vbs, Vcs by which an IPSMS (20)
can be driven by a current command.

[0076] A rotor of the IPMSM (20) is provided with a rotor position
detector (30) to calculate or measure a rotor position and a rotor speed.
The rotor position measured by the rotor position detector (30) is used
for coordinate conversion of the voltage coordinate converter (14) and
the current coordinate converter (18), where the rotor speed is inputted
into the current command correction unit (11).

[0077] The current command correction unit (11) corrects the current
command to allow the IPMSM (20) from the flux weakening control region I
to stably operate at a high speed, a detailed description of which will
be provided later.

[0078] The voltage feedback unit (12) serves to calculate feedback voltage
information used by the current command correction unit (11). The voltage
feedback unit (12) functions to transmit over-modulated voltage
information to obtain a difference of output voltage between the first
coordinate converter (14) and the voltage hunter (15).

[0079] The current controller (13) serves to limit a current command,
which is an output of the current command correction unit (11), to output
d and q-axes voltages on synchronous reference frame. The current
controller (13) is a proportional integral (PI) controller but is not
limited thereto.

[0080] The first coordinate converter (14) uses the position information
of the rotor obtained by the rotor position detector (30) to convert the
output voltage of the current controller (13) to a voltage on a
stationary reference frame. The voltage limiter (15) uses a voltage limit
hexagon to limit the output voltage of the first coordinate converter
(14) to a voltage synthesizable by the inverter unit (16).

[0081] The voltage limit hexagon used by the voltage limiter (15) is a
maximum voltage synthesizable by the inverter unit (16), whereby a
voltage utilization rate of the inverter unit (16) mar be maximized by
the voltage limit hexagon.

[0082] In a case the output voltage of the first coordinate converter (14)
is situated outside of the voltage limit hexagon of the voltage limiter
(15), the voltage synthesized by the inverter unit (16) exists on a
hexagon of the voltage limiter (15), with the voltage of the voltage
coordinate converter (14) not being outputted.

[0083] The inverter unit (16) is a voltage type inverter including a power
semiconductors such as an IGBT (insulated gate bipolar mode transistor)
or a power MOSFET (metal oxide silicon field effect transistor), and
applies the voltage commands (Vas, Vbs, Vcs) for following the current
command to the IPMSM (20).

[0084] The current sensors (17a-17c) measures a phase current between the
IPMSM (20) and the inverter unit (16). The current measured by the
current sensors (17a-17c) is returned to the current controller (13) and
the current command correction unit (11) as a feedback in response to the
coordinate conversion by the second coordinate converter (18). The second
coordinate converter (18) serves to convert the phase current on the
stationary reference frame, measured by the current sensors (17a-17c) to
that on the synchronous reference frame.

[0085] A difference between the conventional driving system of FIG. 1 and
the operating apparatus of FIG. 4 may be summarized in two words. That
is, a current command correction which is an input of the current
controllers (105 and 13), and a final output voltage synthesis applied to
the inverter units (108 and 16).

[0086] In the conventional system of FIG. 1, a command current of the
current controller (105) is obtained from a torque command of the current
command generator (104), the DC-link voltage of the inverter unit (108)
and at least two or more 2-D look-up tables based on rotor speed, whereas
the command current of the current controller (13) is calculated by the
current command correction unit (11) in the operating apparatus of the
present invention.

[0087] Furthermore, in case of final output voltage applied to the
inverter units (108) in the conventional system, the final output voltage
is controlled by an inscribed circle of the voltage limit hexagon,
whereas the voltage limit hexagon is used to limit the final output
voltage in the present invention. Thus, the size of the voltage
synthesized by the operating apparatus of the present invention becomes
relatively greater than that of the conventional system of FIG. 1 to
increase the voltage utilization rate of the inverter and to increase the
output torque as well.

[0088] Now, the current command correction of the operating apparatus of
the present invention based on FIG. 4 will be described. First, a
condition to discriminate the flux weakening control region I and the
flux weakening control region II is provided as below:

[0095] FIG. 5 is a schematic view explaining a concept of Equation 25
according to an exemplary embodiment of the present disclosure.

[0096] J is a constant torque line of Equation 18, K is a current limit
circle. L is a voltage limit ellipse, and M explains a relationship with
Equation 25.

[0097] If Equation 25 satisfied the condition of the following Equation
26, a driving region of IPMSM (20) is discriminated as being changed from
the flux weakening control region I to the flux weakening control region
II.

|(X_norm,Y_norm)(V_norm,W_norm)|=|cos θ|≦ε
[Equation 26]

[0098] Now, the current command correction according to the present
invention will be explained.

[0099] The current command correction unit (11) in FIG. 4 synthesizes the
current command of the flux weakening control region I of IPMSM (20) to
output the d and q-axes current commands on the synchronous reference
frame in order to increase the voltage utilization rate of the inverter
unit (16) in the flux weakening control region II of IPMSM (20).

[0100] At this time, if the condition of Equation 26 is not satisfied, the
current command correction is not performed, and the current command
correction is performed only if the condition of Equation 26 is
satisfied.

[0101] The size of over-modulated voltage returned from the voltage
feedback unit (12) of FIG. 4 may be obtained by the following Equation
27. At this time, the size of voltage synthesized by the inverter unit
(16) is such that the voltage limiter (15) is limited by the voltage
limit hexagon to increase the voltage utilization rate of the inverter
unit (16).

[0103] The voltage used by the current command correction unit (11) may be
obtained by Equation 32 where Equation 27 is integrated and high-pass
filtered.

Δ V mod = 1 s + ω c Δ V
mag [ Equation 32 ] ##EQU00013##

[0104]FIG. 6 is a detailed constructional view illustrating a current
command correction Unit of FIG. 4 according to an exemplary embodiment of
the present disclosure.

[0105] Referring to FIG. 6, the current command correction unit (11) of
the present disclosure includes a current command processing unit (61)
and a current command limiter (62).

[0106] The current command processing unit (61) functions to correct the
current command of the flux weakening control region I to generate a
current command of the flux weakening control region II, and the current
command limiter (62) serves to limit the size of current from the current
command corrected by the current command correction unit (61).

[0107] Now, an operation of the current command processing unit (61) will
be described in the following manner.

[0108] The current command correction by the operating apparatus according
to the present disclosure is to increase the voltage utilization rate in
the flux weakening control region II. Furthermore, a direction of the
current command in the flux weakening control region II faces toward a
center of the voltage limit ellipse, such that the direction is same as
that of Equation 24. Still furthermore, the size of correction during
current command suffices to be proportional to the size of over-modulated
voltage of Equation 27 which may be defined by the following Equation.

[0112] The decision unit, (71) decides the flux, weakening control
regions. To be mere specific, the decision unit (71) decides that a
current correction is not performed for the flux weakening control region
II if the size of the cosine function is greater than a predetermined
value according to Equation 26.

[0113] The direction determination units (72a, 72b) determine the
direction of correction of the current command. The first calculation
units (73a, 73b) perform calculation of Equation 23. The gain calculation
units (74a, 74b) calculate the proportional gains in Equations 35 and 36,
and the first limit units (75a, 75b) limit the size of the current
change.

[0114] The section defining units (76a, 76b) define a hysteresis section
for dividing the flux weakening control region I and the flux weakening
control region II. The adding units (77a, 77b) output a final current
command by adding a reference current to an output of the section
defining units (76a, 76b).

[0115] Now, the current command limiter of FIG. 6 will be described in
detail.

[0116] The current command corrected by the current command processing
unit (61) of FIG. 6 must exist within a current range outputtable by the
inverter unit (16).

[0117] At this time, the limitation of current command provides priority
to the d-axis current, and the d-axis current on the synchronous
reference frame corrected by Equation 33 is outputted within the size of
the rated current on a priority base, where a q-axis current command
selects as a permissible range a balance where a size of d-axis current
is deducted from the rated current.

[0118] FIG. 8 is a detailed constructional view illustrating a current
command limiter of FIG. 6, according to an exemplary embodiment of the
present disclosure.

[0119] Referring to FIG. 8, the current command limiter (62) according to
the present disclosure comprises a second limiter (81), a second
calculator (82), to third calculator (83) and a third limiter (84).

[0120] The second limiter (81) limits in such a manner that the corrected
d-axis current outputted by the adding unit (77a) exists within an
allowable current range. The second calculator (82) obtains a positive
q-axis maximum allowable current range from the d-axis current outputted
from the second limiter (81) and the allowable current.

[0121] The third calculator (83) calculates a negative q-axis maximum
allowable current range. The third limiter (84) limits the size of q-axis
current based on the second and third calculators (82. 83).

[0122] The operation in the flux weakening control region II of IPMSM
according to the present disclosure is realized by correction of current
corn using a difference between an output voltage of a current controller
(13) and a voltage actually synthesized by an inverter unit (16).

[0123] As apparent from the foregoing, the apparatus for operating,
interior permanent magnet synchronous motor according to the present
disclosure has an industrial applicability in that a difference between
two voltages is minimized using a difference between an output voltage of
a current control unit and a voltage actually synthesized by an inverter
unit, and dispensing with a prior-prepared look-up table, all the voltage
limit hexagons are used to increase a DC-link voltage utilization rate of
the inverter unit relative to size of the voltage synthesized by the
inverter unit, and a current command is corrected to as direction holding
a torque at a predetermined level, whereby a maximum torque can be
outputted even when an IPMSM is driven at a high speed.

[0124] More particularly, various variations and modifications are
possible in the component parts and/or arrangements of subject
combination arrangement within the scope of the disclosure, the drawings
and the appended claims. In addition to variations and modifications in
the component parts and/or arrangements, alternative uses will also be
apparent to those skilled in the art,